<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <h2 id="h2">0</h2>
  <button id="minus">-1</button>
  <button id="add">+1</button>

  <script>
    let minus = document.getElementById("minus");
    let add = document.getElementById("add");
    let h2 = document.getElementById("h2");

    let count = 0
    minus.addEventListener("click", () => {
      count--
      h2.innerText = count
    })
    add.addEventListener("click", () => {
      count++
      h2.innerText = count
    })
  </script>
</body>
</html>